This invention relates to a crystalline zeolitic material having the framework topology of tschxc3x6rtnelite, an empirical formula of mA2/11O: Al2O3 : ySiO2 where A is a cation such as lithium. The invention also relates to an air separation process using the zeolite.
Zeolites are crystalline aluminosilicate compositions which are microporous and which have a three-dimensional oxide framework formed from comer sharing AlO2 and SiO2 tetrahedra. Numerous zeolites, both naturally occurring and synthetically prepared are used in various industrial processes. Zeolites are characterized by having pore openings of uniform dimensions, having a significant ion exchange capacity, and being capable of reversibly desorbing an adsorbed phase which is dispersed throughout the internal voids of the crystal without significantly displacing any atoms which make up the permanent zeolite crystal structure.
The number of synthetic zeolites is well over a hundred as evidenced by the Atlas of Zeolite Structure Types published by the International Zeolite Association (IZA). As is well known, zeolites are distinguished from each other on the basis of their composition, crystal structure and adsorption properties. One method commonly used in the art to distinguish zeolites is x-ray diffraction.
A mineral discovered in 1993 in the Bellberg volcano, Eifel, Germany was found to be a new zeolite which was named tschxc3x6rtnerite. The structure was reported by H. Effenberger et al. in American Mineralogist, Vol. 83, pp. 607-617, 1998, in which the ideal empirical formula was found to be Ca4 (K, Ca, Sr, Ba)3 Cu3 (OH)8 [Si12 Al12 O48]. xH2O, x=20. It was also found that the crystal morphology was cubic with a=31.62 xc3x85. Although tschortnerite has a very large cage, the largest pore openings are only single and double eight rings. Also the presence of extra-framework copper diminishes the utility of natural tschxc3x6rtnerite (along with the fact that only 1 mg of tschxc3x6rtnerite has been found). In view of tschxc3x6rtnerite""s structure, it would be desirable to prepare a synthetic version, without copper, for use in various separation processes.
As stated, the present invention relates to a crystalline zeolitic composition having a microporous framework structure containing AlO2 and SiO2 tetrahedral units and an empirical formula on an anhydrous and as synthesized basis in terms of molar oxide ratios of:
mA2/11O: Al2O3: ySiO2xe2x80x83xe2x80x83(I)
where A is an exchangeable cation selected from the group consisting of alkali metals, alkaline earth metals, amines, quaternary ammonium ions and mixtures thereof, xe2x80x9cmxe2x80x9d is the mole ratio of the oxide of A to Al2O3 and varies from about 0.8 to about 1.5, xe2x80x9cnxe2x80x9d is the valence of A and xe2x80x9cyxe2x80x9d is the mole ratio of SiO2 to Al2O3, the composition characterized in that it has the crystalline structure of TSC and a cubic crystalline cell with a value of a=30 to about 33 xc3x85.
Another embodiment is a process for separating one molecular species from a mixture of molecular species comprising contacting the mixture with the zeolitic composition described above.
A specific embodiment is separating nitrogen from air by contacting air with the above described zeolite to adsorb the nitrogen onto the zeolite.
These and other objects and embodiments will become more apparent after the detailed description of the invention.